As a conventional fine processing technology for semiconductors, information recording media, and the like, a dry etching method is known which includes a mask layer processing step of forming a mask layer having a predetermined pattern on a layer to be processed, and a layer-to-be-processed processing step of removing an exposed portion of the layer to be processed by dry etching so as to process the layer to be processed in the aforementioned pattern.
There are various types of dry etching. Reactive ion etching, that is one type of dry etching, can increase a selection ratio of an etching rate of the layer to be processed and an etching rate of the mask by appropriately selecting types of a reactive gas and a material for the mask. Thus, reactive ion etching can make the mask layer thinner and process a fine pattern. For that reason and the like, reactive etching is widely used at present.
Reactive ion etching is a technology that has developed mainly in the field of semiconductor fabrication. This technology can be also used in other fields such as fabrication of an information recording medium including a magnetic layer, for example (see Japanese Patent Laid-Open Publication No. Hei 12-322710, for example).
However, although the layer to be processed can be patterned in a fine pattern by the technique of dry etching, it is difficult to process the layer to be processed 100 in a shape in which its peripheral portion 100A corresponding to the outline of the pattern is angular, as shown in FIG. 21(A). In fact, the peripheral portion of the layer to be processed is processed in a rounded shape. Thus, a certain degree of disagreement occurs between a desired processed shape and the actually processed shape.
More specifically, in dry etching, not only the layer to be processed is removed, but also the mask layer on the layer to be processed is etched and removed little by little. In the etching of the mask layer 102, as shown in FIG. 21(B), a peripheral portion 102A is removed faster than other portions. Thus, as shown in FIG. 21(C), the peripheral portion 100A of the layer to be processed 100 is exposed from the mask layer 102 faster than other portions of the layer to be processed 100. Therefore, the layer to be processed 100 is removed faster in the peripheral portion 100A than in the other portions, so that the peripheral portion 100A is processed in a rounded shape, as shown in FIG. 21D. Such a phenomenon usually occurs in dry etching. Especially, such a phenomenon is more apparent in reactive ion etching.
In dry etching, a part of ions is incident on the layer to be processed at an angle with respect to that layer. Therefore, a side face of the layer to be processed 100 is in the shadow of the mask with respect to the ions incident on the layer to be processed at an angle, so that it is processed to be tapered.
As the pattern becomes finer, an effect of the aforementioned disagreement of the processed shape on properties of a product and the like tends to become relatively larger. For example, in an information recording medium and an apparatus for recording and/or reproducing information, the effect of the aforementioned disagreement of the processed shape on the properties of the product and the like, becomes a problem in many cases. Thus, needs of a dry etching technique that can process the layer to be processed in a shape in which its peripheral portion is angular have increased.
The aforementioned problem can be avoided if the mask layer having a sufficient thickness is formed on the layer to be processed in advance, considering that the peripheral portion of the mask layer is removed faster than the other portions. However, the mask layer is also processed by dry etching in a predetermined pattern generally, so that the side face of the patterned mask layer is tapered. Thus, in the case where the pitch of the pattern is small, when the mask layer is thick, a concave portion having a V-shaped cross section is formed in the mask layer or the layer to be processed by continuous side faces of the mask layer or the layer to be processed. After the V-shaped concave portion is formed, etching no longer progresses. Thus, it may be impossible to process the layer to be processed to a desired depth.